The present invention relates to a tool for drilling/routing of printed circuit board materials. By alloying the binder phase with Ru in combination with the use of fine grained Co-powder the properties have been improved.
Cemented carbide containing Ru as binder phase alone or in combination with the conventional Co and/or Ni is known in the art. For example, AT 268706 discloses a hard metal with Ru, Rh, Pd, Os, Ir, Pt and Re alone or in combination as binder phase. U.S. Pat. No. 4,574,011 discloses a hard metal composition for ornamental purposes with a binder phase of Co, Ni and Ru. GB 1309634 discloses a cutting tool with a Ru binder phase. GB 622041 discloses a hard metal composition a Co+Ru binder phase.
The routing of Printed Circuit Board materials requires a wide range of properties from the tool material in order for it to perform successfully. These include a hardness in excess of 2000 HV, a resistance to edge chipping that is best defined by a fracture toughness in excess of 8 MPam1/2, a resistance to chemical attack from the resins included in printed circuit boards and a sharp as possible a cutting edge. Some of these requirements conflict, for instance the high hardness tends to mean a reduced edge toughness. The new products for this application can, therefore, require a reduced WC grain size to produce a higher hardness with reduced toughness. However, if this is combined with an increase in cobalt content an increased toughness can be achieved for the same hardness. This also results in a sharper cutting edge, which is required.
The invention is primarily concerned with the addition of ruthenium to submicron grades of cemented carbide. The levels of addition vary between 5 and 35, preferably between 15 and 30, wt-% of the binder content with the best results obtained at about 25 wt-%. For best effects the cobalt used should be of the fine grain size cobalt powder having deagglomerated spherical grains of about 0.4 xcexcm average grain size and with a narrow grain size distribution. Preferably the cobalt powder is polyol cobalt. The cobalt contents to which this addition can be made should vary from 5-12%, preferably 5-8. The average WC grain size shall be  less than 0.8 xcexcm, preferably  less than 0.4 xcexcm. The cemented carbide of the invention is preferably a straight WC+Co grade but it may also contain  less than 5 wt-% gammaphase.
In order to obtain the submicron WC grain size VC+Cr3C2 is added. Because the Ru also acts as a mild grain growth inhibitor an addition of  less than 0.9 wt % VC+Cr3C2 is generally satisfactory. Particularly good results are obtained if the VC/Cr3C2 ratio in wt % is 0.2-0.9, preferably 0.4-0.8, most preferably 0.6-0.7. Preferably sintering is performed using gas pressure sintering also referred to as sinter-HIP.
The invention also relates to the use of a cemented carbide with submicron WC grain size and with a binder phase containing 10-30 wt-% Ru as a tool for drilling/routing of printing circuit board materials.
The present invention further relates to a method of making a cemented carbide body comprising one or more hard constituents and a binder phase based on cobalt, nickel and/or iron by powder metallurgical methods milling pressing and sintering of powders forming hard constituents and binder phase whereby said binder phase contains 10-30 wt-% Ru. At least part of the binderphase powder consists of non agglomerated particles of spheroidal morphology of about 0.4 xcexcm average grain size and with a narrow grain size distribution wherein at least 80% of the particles have sizes in the interval xxc2x10.2x provided that the interval of variation (that is 0.4x) is not smaller than 0.1 xcexcm.
The advantages offered by the ruthenium additions are as mentioned a further element of grain growth refinement, an increase in resistance to chemical attack and a strengthening of the binder phase without significantly affecting the edge toughness due to the increase in cobalt content used.